This invention relates to an ink, an ink set, and an ink jet recording method that are particularly favorable for ink jet recording.
As is commonly known, ink jet recording is a method in which printing is performed by causing droplets of ink to fly out and adhere to a recording medium such as paper. This printing method allows images of high resolution and quality to be printed quickly and simply with an inexpensive apparatus, and particularly in the field of color printing, this image formation method has in recent years been the subject of technological development as an alternative to photography.
When a color image is formed by ink jet recording, the printing is performed using inks of at least the three primary colors of magenta, yellow, and cyan, but more recently it has become commonplace to obtain a more detailed image by using light and dark inks of different density for the magenta ink and cyan ink in order to obtain a higher-quality image. It is important that these inks themselves have excellent color reproducibility, and achieving good color reproducibility is also important when two or more inks selected from among magenta ink, yellow ink, and cyan ink are printed on top of each other and red, green, blue, and black are formed.
In the past these ink-jet inks have mainly consisted of water-based inks, in consideration of odor and safety (e.g., fire hazards). Among the properties required of these inks are that their viscosity, surface tension, and other such physical properties be within a suitable range, that they have excellent storage stability and do not clog the nozzle, that they give a high-density recorded image, and that they have excellent light fastness, water resistance, and moisture resistance.
Most of these performance requirements can be satisfied by using a water-based ink in which the main solvent is water or a mixture of water and a water-soluble organic solvent, but color, clarity, light fastness, water resistance, moisture resistance, and so forth are greatly affected by the colorant, and many different dyes have been researched up to now.
In particular, with a color recording method that makes use of inks of a number of colors, all of the inks used must have uniform characteristics. Fading and color changes caused by light (sunlight, fluorescent light, etc.) is particularly pronounced with magenta dyes, more so than with other dyes (cyan and yellow dyes). Therefore, the inferior light fastness of a magenta ink compared to that of other inks means that not only will this inferiority be apparent with the magenta ink by itself, but also in secondary colors (such as red and blue) expressed by superposing yellow ink or cyan ink, and this leads to a change in the color of the overall image in recorded material, and a loss of quality.
Acid dyes that are highly water soluble and have good color development, such as C.I. Acid Red 52, 249, and 289, have been known in the past as magenta dyes for use in ink jet recording, but although nozzle clogging tended not to occur when these dyes were used alone because of their high water solubility, their light fastness performance was extremely poor.
In response to these requirements, Japanese Laid-Open Patent Applications H6-228447, H8-90211, H8-73791, H10-306221 and so forth have disclosed a magenta dye ink with excellent light fastness, water resistance, moisture resistance, color, clarity, and so on.
Still, light fastness, water resistance, vivid color and color reproducibility, nozzle clogging resistance, and so forth could not all be satisfied at the same time with inks in which these magenta dyes proposed in the past were used.
It has also been disclosed, in Japanese Laid-Open Patent Applications H5-214259 and 2001-115072, that excellent color reproducibility and light fastness can be obtained even with secondary or tertiary colors by using an ink set that makes use of a specific dye set.
However, light fastness, water resistance, vivid color and color reproducibility, nozzle clogging resistance, and so forth could not all be satisfied at the same time with inks in which these ink sets proposed in the past were used.
It is therefore an object of the present invention to provide an ink, an ink set, and a recording method with which light fastness, water resistance, vivid color and color reproducibility, nozzle clogging resistance, and so forth can all be satisfied.
The stated object is achieved with the present invention as follows.
The magenta ink of the present invention comprises at least water, a water-soluble organic solvent, a first dye, and a second dye, the first dye has a structure expressed by the following General Formula I, the second dye is a dye having a structure expressed by the following General Formula II and/or one or more types of dye selected from among C.I. Acid Violet 9 and 30 and C.I. Acid Red 50, 52, and 289, and the weight ratio of first dye to second dye is 5:1 to 1:5. 
M is H, Li, Na, K, ammonium, or an organic amine
R1 is H, Cl, or 
X is an anilino group substituted with at least one SO3M
Y is OH, Cl, or a morpholino group
R2 is H, CH3, Cl, or SO3M
The dyes in the ink of the present invention may be water-soluble dyes.
It is preferable for the total amount of dye contained in the ink to be 0.5 to 5 wt % of the total ink weight.
The ink of the present invention may contain a glycol ether of a lower alkyl and/or an acetylene glycol-based nonionic surfactant.
The ink of the present invention may be such that the above-mentioned glycol ether of a lower alkyl includes at least one type of compound selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, and dipropylene glycol monobutyl ether.
The ink of the present invention may contain the glycol ether of a lower alkyl in an amount of 3 to 30 wt % of the total ink weight.
The ink of the present invention may contain the acetylene glycol-based nonionic surfactant in an amount of 0.1 to 3 wt % of the total ink weight.
The ink set of the present invention is an ink set composed of at least a dye, a water-soluble organic solvent, and water, wherein said ink set is composed of the magenta ink according to claim 1, a yellow ink containing a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of from 1:3 to 3:1, or a dye containing C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of from 1:4 to 4:1, and a cyan ink containing C.I. Direct Blue 86 and/or C.I. Direct Blue 199.
In the ink set of the present invention, the respective dyes of the magenta ink, yellow ink, and cyan ink may be water-soluble dyes.
In the ink set of the present invention, it is preferable for the total amount of dye contained in the magenta ink to be 1 to 4 wt % of the total ink weight, the total amount of dye contained in the yellow ink to be 0.5 to 4 wt % of the total ink weight, and the total amount of dye contained in the cyan ink to be 1 to 4 wt % of the total ink weight.
The ink set of the present invention may contain a glycol ether of a lower alkyl and/or an acetylene glycol-based nonionic surfactant.
The ink set of the present invention may be such that the above-mentioned glycol ether of a lower alkyl includes at least one type of compound selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, and dipropylene glycol monobutyl ether.
The ink set of the present invention may contain the glycol ether of a lower alkyl in an amount of 3 to 30 wt % of the total ink weight.
The ink set of the present invention may contain the acetylene glycol-based nonionic surfactant in an amount of 0.1 to 3 wt % of the total ink weight.
The recording method of the present invention is an ink jet recording method in which printing is performed by discharging droplets of ink and causing them to adhere to a recording medium, wherein the above-mentioned ink is used as the ink.
Also, the recording method of the present invention is an ink jet recording method in which at least a magenta ink, a yellow ink, and a cyan ink are used to form a color image, wherein the ink set is used.
When ink jet recording is performed using the ink or ink set pertaining to the present invention, the resulting image will have good light fastness, as well as excellent color, water resistance, moisture resistance, color reproducibility, and other characteristics. Preferred embodiments of the present invention will now be given to describe the present invention in further detail.
The magenta ink used in the present invention includes a first dye, which is a dye having the structure expressed by General Formula I, and a second dye, which is a dye having the structure expressed by General Formula II and/or one or more types of dye selected from among C.I. Acid Violet 9 and 30 and C.I. Acid Red 50, 52, and 289.
For the sake of safety and other such considerations, the dye having the structure expressed by General Formula I used in the present invention, and the dye having the structure expressed by General Formula II, and the C.I. Acid Violet 9 and 30 and C.I. Acid Red 50, 52, and 289 are preferably water-soluble dyes that will dissolved in a water-soluble ink.
Specific examples of the dye expressed by General Formula I are given below, but this list is not intended to be comprehensive. 
Specific examples of the dye expressed by General Formula II are given below, but this list is not intended to be comprehensive, either. 
Examples of dyes that can be used as the second dye, either alone or as a mixture with a dye having the structure expressed by General Formula II, include xanthene dyes selected from among C.I. Acid Violet 9 and 30 and C.I. Acid Red 50, 52, and 289.
Adequate light fastness will not be obtained when these xanthene dyes are used alone, but excellent light fastness can be obtained by mixing with a dye having the structure expressed by General Formula I, and the color development of a magenta ink will also be improved.
As to the amount in which the dyes are added, it is preferable for the dye having the structure expressed by General Formula I (the first dye) and the dye having the structure expressed by General Formula II and/or one or more types of dye selected from among C.I. Acid Violet 9 and 30 and C.I. Acid Red 50, 52, and 289 (the second dye) to be used in a weight ratio of first dye:second dye=5:1 to 1:5, (more preferably, a weight ratio of first dye:second dye=3:1 to 1:1) and for the amount to be from 0.5 to 5 wt % of the total ink weight (and more preferably, 1 to 4 wt % of the total ink weight). Specifically, keeping the amount within this range ensures the reliability of the ink-jet ink, such as its printing density and clarity, clogging resistance, and discharge stability. Furthermore, an ink with excellent solubility in water, and excellent clarity and light fastness can be provided.
The yellow ink that can be used in the ink set pertaining to the present invention in combination with the above-mentioned magenta ink preferably contains a dye including C.I. Direct Yellow 86 and C.I. Direct Yellow 132 in a weight ratio of 1:3 to 3:1, or a dye including C.I. Direct Yellow 86 and C.I. Direct Yellow 173 in a weight ratio of 1:4 to 4:1, in an amount of 0.5 to 4 wt % of the total ink weight. Keeping the amount within this range ensures the reliability of the ink-jet ink, such as its printing density and clarity, clogging resistance, and discharge stability. Furthermore, an ink with excellent solubility in water, and excellent clarity and light fastness can be provided.
The cyan ink that can be used in the ink set pertaining to the present invention in combination with the above-mentioned magenta ink preferably contains C.I. Direct Blue 86 and/or C.I. Direct Blue 199 in an amount of 1 to 4 wt % of the total ink weight. Keeping the amount within this range ensures the reliability of the ink-jet ink, such as its printing density and clarity, clogging resistance, and discharge stability. Furthermore, an ink with excellent solubility in water, and excellent clarity and light fastness can be provided.
The liquid medium in which the above-mentioned specific dyes of the magenta ink, yellow ink, and cyan ink are dissolved is preferably a mixture of water and a water-soluble organic solvent. The water here is preferably deionized water, rather than ordinary water which contains various ions, and the water-soluble organic solvent is preferably a solvent with low volatility from the standpoint of minimizing clogging. Examples include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, 1,5-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol, glycerol, and other such polyhydric alcohols; ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and other such glycol ethers; formamide, dimethylformamide, diethanolamine, triethanolamine, 1,3-dimethyl-2-imidazolidinone, 2-pyrrolidone, N-methyl-2-pyrrolidone, and other such nitrogen-containing solvents; and thiodiglycol, dimethyl sulfoxide, and other such sulfur-containing solvents. The present invention is not limited to these compounds, however, and a plurality of types of water-soluble organic solvent may also be contained. As to the content thereof, a range of 3 to 50 wt % with respect to the total ink weight is suitable for an ink-jet ink. Keeping the content to at least 3 wt % prevents the nozzle tip from clogging, while keeping it to no more than 50 wt % prevents a decrease in the dryability of the recorded image or the bleeding of the recorded image, which would lead to a drop in print quality.
Adding glycol ether of a lower alkyl is effective with respect to the dryability and bleeding of the ink. Particularly suitable examples include diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, and dipropylene glycol monobutyl ether, and the added amount thereof is preferably selected from a range of 3 to 30 wt %. Keeping the amount to at least 3 wt % is effective with respect to dryability and bleeding, while keeping it to no more than 30 wt % prevents excessive bleeding and maintains print quality, so it is preferable for the amount to be within the above range.
An acetylene glycol-based nonionic surfactant is also effective with respect to the dryability and bleeding of the ink. Specific examples include Olfin E1010, Olfin STG, and Surfinol 104E (the above are products of Nisshin Chemical). The added amount thereof is preferable between 0.1 and 3 wt % with respect to the total ink weight.
Even more preferably, a sharp image with no bleeding can be obtained by using the above-mentioned acetylene glycol-based nonionic surfactant together with glycol ether.
The water content here is determined over a wide range by the type of the above-mentioned solvent component, the composition thereof, and the desired characteristics of the recording liquid, but is generally within a range of 10 to 70 wt % of the total ink weight.
In addition to the above-mentioned components, in order to impart the desired performance to the ink of the present invention, the ink may contain as necessary sodium alginate, polyvinyl alcohol, or another viscosity regulator, or sodium hydroxide, potassium hydroxide, lithium hydroxide, or another hydroxide of an alkali metal, or ammonium phosphate, or another such pH buffer or other pH regulator, or a preservative, rustproofing agent, antioxidant, mildew inhibitor, fungicide, chelating agent, or other such additive.
With the ink jet recording method pertaining to the present invention, it is possible to obtain excellent color reproducibility in magenta, yellow, and cyan, as well as good light fastness in primary, secondary, and tertiary colors.
Also, the ink jet recording method of the present invention involves using the above-mentioned ink to perform recording, and can make use of any conventional type of head discharge system, but a particularly outstanding ink jet recording method can be realized with methods in which the vibration of a piezoelectric element is utilized to discharge droplets, or methods in which thermal energy is utilized.